Irradiation of Ni-Cu ferrite nanoparticles by 241Am-9Be source and investigation of their structural and magnetic properties using positron annihilation spectroscopy

Single-phase Ni-Cu ferrite nanoparticles have been prepared by sol-gel method and exposed using an Am-Be source for time periods of one and two months. The effects of irradiation on structure and magnetic properties of prepared nanoparticles are investigated by X-ray diffraction, positron annihilation spectroscopy and vibrating sample magnetometer. The X-ray measurements showed that unirradiated and irradiated samples have cubic spinel structure and variation of structural parameters with irradiation is nonuniform. The positron annihilation measurements showed that the main effect of irradiation on samples is variation in momentum distribution of core electrons in metallic cations. The magnetic measurements represent that irradiation cause an increase in saturation magnetization and a decrease in coercivity. The increase in saturation magnetization is attributed to cation redistribution because of atomic displacement. The decrease in coercivity is attributed to the variation of magnetocrystalline anisotropy constant due to the effect of irradiation on the core electrons of cations.